Dimorphism in Fungi

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Dimorphism in Fungi
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Professor Glenn S. Bulmer Ph.D. Manila/Beijing/Xin
jiang
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Definition Fungi that have 2 different
morphological forms Di two Morphism
forms (the way you see something)
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Dimorphism is usually seen as a hyphal (spores)
at room temperature (RT), ca 24C and a yeast at
35C. But, there are exceptions, eg., same forms
at both RT and 35C but different in vivo (same
in vitro and different in vivo).
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In all cases the hyphal/spores are the infectious
particles, which live in nature, and the yeast
(or other in vivo form) is the pathogenic phase.
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Examples of diseases caused by dimorphic fungi
are histoplasmosis, blastomycosis,
sporotrichosis, paracoccidioidomycosis,
coccidioidomycosis, penicilliosis,
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Let us look at some examples Histoplasma
capsulatum
The spore (infectious) phase grown at 24 C.
The yeast (pathogenic) phase grown at 35 C.
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Sporothrix schenckii.
The yeast (pathogenic) phase grown at 35 C.
The spore (infectious) phase grown at 24 C.
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Coccidioides immitis
In tissue
Culture 24C or 35C
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Blastomyces dermitititis
35 C
24 C
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In tissue intracellular yeasts.
Both forms of Penicillum marneffei
Culture at 24 C
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Cryptococcus neoformans A monomorphic pathogen
Always a yeast at 24 C, 35 C and in vivo.
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Candidiasis Monomorphic or Dimorphic?
Regardless of conditions it grows with a mixture
of yeast and pseudohyphae.
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Importance (Implications) of dimorphism 1). The
in vivo form is not infectious but in vitro form
is dangerous (eg., spores) for H. capsulatum,
C. immitis and possibly Penicillum marneffei. 2).
Mechanism to escape bodys defense. 3).
Different antigens, eg., problem in serology,
immunology, vaccines, skin test reagents etc. 4).
Antifungal agents----to attack hyphal/spore form
or in vivo form. 5). If the RT form will not
produce characteristic spores, growth of the
yeast form at 35 C proves dimorphism of a
pathogen. 6). Important in
histopathology---know what to look for !!!
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Dimorphism is unique in pathogenic fungi. It is
very important. You must know about it if you
want to be a good student of Fungus Diseases.
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Thank You!